Display omitted •Graphene oxide were used as nanoplatelets into UV-curable epoxy resin.•Cationic UV–curing was performed for the different formulations.•A clear enhancement of the water vapor transmission rate was measured for composites coatings. In this paper we investigated the improvement of water-vapor barrier properties of an UV-cured epoxy film containing graphite oxide nanoplatelets. Graphene platelets were successfully dispersed in the epoxy resin and cured by UV-irradiation. Good performances in increasing water vapor barrier properties at a very low filler loading are obtained: the permeability decreased of about 40% with a 0.5wt.% of GOx and of about 60% with a 1.0wt.% of GOx. These good results are attributed to a homogeneous filler dispersion, as clearly shown by TEM microscopy.